Mechanical warewashing machines have been common in the institutional and household environments for many years. Such automatic warewashing machines clean dishes using two or more cycles which can include initially a wash cycle followed by a rinse cycle. Such dishwashers can also utilize soak cycle, prewash cycle, scrape cycle, second wash cycle, a rinse cycle, a sanitizing cycle and a drying cycle, if required. Such cycles can be repeated if needed and additional cycles can be used. After passing through a wash, rinse and dry cycle, dishware, cups, glasses, etc., can exhibit spotting that arises from the uneven draining of the water from the surface of the ware after the rinse step. Spotting is aesthetically unacceptable in most consumer and institutional environments.
In order to substantially prevent the formation of spotting rinse agents have commonly been added to water to form an aqueous rinse which is sprayed on the dishware after cleaning is complete. The precise mechanism through which rinse agents work is not established. One theory holds that the surfactant in the rinse aid is absorbed on the surface at temperatures at or above its cloud point, and thereby reduces the solid-liquid interfacial energy and contact angle. This leads to the formation of a continuous sheet which drains evenly from the surface and minimizes the formation of spots. Generally, high foaming surfactants have cloud points above the temperature of the rinse water, and, according to this theory, would not promote sheet formation, thereby resulting in spots. Moreover, high foaming materials are known to interfere with the operation of the warewashing machine. Common rinse aid formulas are used in an amount of less than about 1,000 parts preferably less than 500 parts, commonly 50 to 200 parts per million of active materials in the aqueous rinse. Rinse agents available in the consumer and institutional markets comprise liquid or solid forms which are typically added to, dispersed or dissolved in water to form an aqueous rinse. Such dissolution can occur from a rinse agent installed onto the dish rack. The rinse agent can be diluted and dispensed from a dispenser mounted on or in the machine or from a separate dispenser that is mounted separately but cooperatively with the dish machine.
Many rinse agents comprise a polyalkylene oxide copolymer preferably ethylene oxide/propylene oxide block copolymer. In such materials, the ethylene oxide block tends to be hydrophilic while the propylene oxide blocks tend to be hydrophobic producing a separation of hydrophilic and hydrophobic groups on the surfactant molecule. Those skilled in the art of formulating nonionic based rinse agents have formed a belief that an EO/PO block copolymer must have a cloud point (measured in a 1 wt-% aqueous solution) substantially less than the use temperature of the aqueous rinse and exhibit good wetting properties to obtain sheeting. Such belief is borne out in a review of promotional material related to low cloud point block copolymers. Block copolymers suggested for use in aqueous rinse aids typically comprise low molecular weight (less than about 5,000) and display low cloud points (less than about 40.degree. C. using a 1 wt-% aqueous solution). The common belief in the rinse aid art is that high cloud point, high molecular weight block copolymers would not exhibit good sheeting properties and would have substantial foaming problems. Further, a substantial need has arisen for environmentally compatible rinse agent compositions. Rinse additives are well known to the trade and have been in use for thirty or more years. However there is an unmet need for rinse additives that are made entirely of food additive materials. Formulation of successful compositions using the limited range of materials approved as food additives is a very challenging situation since using only food additive materials greatly limits what can be used in the formulation. Further, such formulations are very unique in that few combinations will work.
Surprisingly, we have found that high molecular weight, high cloud point materials can be effectively defoamed with effective food additive defoamer materials to form rinse additives which yield desirable continuous sheets on the ware and provide an extra degree of safety if they leave any residue on the cleaned ware. In our research on developing rinse agents, we find that the nonionic agents of the invention are surprisingly good sheeting agents even though they have high cloud points and generate significant volumes of foam in use. Those skilled in the art find that surfactants in rinse aids require both effective wetting agent properties and low foaming properties. Traditionally, rinse agents contain nonionic surfactants with relatively low cloud points since these materials exhibit little foam above the cloud point. The nonionics of the invention have cloud points above 100.degree. C. measuring a 1 wt-% aqueous solution and were consistently considered to be poor candidates for rinse agents because high cloud points indicate poor sheeting properties. However, we have found surprisingly that although these materials foam significantly, they have acceptable sheeting properties at approximately 200 parts, preferably 100 parts, of the nonionic polyether per million parts of rinse composition. Moreover, we have found that the use of certain classes of defoamers in combination with the nonionics of the invention yield rinse agent materials with very low foaming properties that perform very well in sheeting tests. We have found food additive defoamers that can be combined with food additive nonionic block copolymer materials. Most high foaming nonionic materials are generally hydrophilic and quite water soluble. On the other hand, adequate defoaming materials tend to be quite hydrophobic. Hydrophilic and hydrophobic materials are generally incompatible at high concentrations in a concentrated form. In many warewashing apparatus, defoaming materials are often added directly to the rinse aid or other aqueous compositions at the point of use. The defoamer not only suppresses the foaming nature of the high cloud point nonionic material but appears to make the nonionic material behave like the low cloud point material in forming an evenly draining, continuous film. This property of the combination is unexpected. The rinse agents can be diluted to form an effective aqueous rinse with a water miscible aqueous diluent. The rinse agents of the invention can also take the form of a liquid rinse agent or a cast solid rinse agent material.
Haslop et al., U.S. Pat. No. 4,618,446, teaches a variety of ingredients for use in spherical liquid detergent compositions.
Haslop et al., U.S. Pat. No. 4,793,943, teaches a variety of ingredients useful for making liquid detergent compositions.
Akred et al., U.S. Pat. No. 4,871,467, teaches a variety of compositions and materials used to form non sedimenting liquid detergent compositions.
Aronson et al., U.S. Pat. No. 5,045,225, teaches a combination of hydrocarbon oils and silicone compositions as antifoam materials.
Gentle et al., U.S. Pat. No. 5,073,298, teaches silicone silicate based defoaming compositions.
Chun et al., U.S. Pat. No. 5,133,892, teaches machine dishwashing detergent tablets having timed release of enzyme and chlorine bleach and a variety of other ingredients used in making the detergent composition.
Tsukada, Japanese Patent Application Publication Kokai 49-126,703, teaches carbohydrate aliphatic ester rinse agents.
Miura et al., Japanese Patent Application Publication Kokai 50-62,211, teaches polyhydric alcohol containing rinse agents.
Miura et al., Japanese Patent Application Publication Kokai 51-68,608, teaches polyol aliphatic ester containing rinse agent compositions.
Suzuki et al., Japanese Patent Application No. 86-131,272, teaches a rinse agent comprising a polyethoxylated sorbitan fatty acid ester glycerol and a sugar alcohol.
Suzuki et al., Japanese Patent Application No. 86-161,193, teaches a similar material.
Nantaku, Japanese Patent Application No. 59-187,096, teaches a polyglycerine ester of a C.sub.6-8 fatty acid containing rinse agent.
Wilson et al., "Rinse Additives for Machine Dishwashing", Soap and Chemical Specialties, pp 48 et seq. (February 1958), discusses the basic technology regarding rinse agent formulation.
None of the prior art material combine the preferred high cloud point, high foaming surfactants with an appropriate defoamer to achieve a rinse agent that can be diluted into an aqueous rinse providing low foaming sheeting properties.